Why is dU (change in internal energy)= heat absorbed (Q[v])at constant Temperature and Volume.? And why is dH (enthalpy change)= heat change (Q[p]) at constant temperature and pressure? I do understand why constant pressure and volume is specified but why should the temperature be constant in both cases? shouldn't the first case imply dU=0 at constant temperature?

Question

Why is dU (change in internal energy)=  heat absorbed (Q[v])at constant Temperature and Volume.? And why is dH (enthalpy change)=  heat change (Q[p]) at constant temperature and pressure? I do understand why constant pressure and volume is specified but why should the temperature be constant in both cases? shouldn't the first case imply dU=0 at constant temperature?

anonymous · Answer

$$\Delta U=Q+W $$
$$W=0$$

joannablackwelder · Answer

W = -PΔV

joannablackwelder · Answer

I think we assume constant temperature so that we can calculate the total energy change without losing internal energy due to heat lost or gained.

anonymous · Answer

Ok guys what is your educational qualification . Tell me so I can give answer as u can understand. Ok have a nice day